Multispectroscopic studies on the interaction of maltol,a food additive,with bovine serum albumin

The interaction between maltol, a food additive, and bovine serum albumin (BSA) under simulated physiological conditions was investigated by fluorescence, UV–Vis absorption, circular dichroism (CD) and Fourier transform infrared (FT-IR) spectroscopy. The results suggested that the fluorescence quenching of BSA by maltol was a static procedure forming a maltol–BSA complex. The positive values of enthalpy change and entropy change indicated that hydrophobic interactions played a predominant role in the interaction of maltol with BSA. The competitive experiments of site markers revealed that the binding of maltol to BSA mainly took place in subdomain IIA (Sudlow site I). The binding distance between maltol and BSA was 3.01 nm based on the Förster theory of non-radioactive energy transfer. Moreover, the results of UV–Vis, synchronous fluorescence, CD and FT-IR spectra demonstrated that the microenvironment and the secondary structure of BSA were changed in the presence of maltol.     

DNA binding studies of 2-tert-butylhydroquinone (TBHQ) food additive

The interaction of native calf thymus DNA with 2-tert-butylhydroquinone (TBHQ) in 10 mM Tris–HCl aqueous solutions at neutral pH 7.4, has been investigated by spectrophotometric, spectrofluorometric, voltammetric and viscosimetric techniques. It is found that TBHQ molecules could intercalate between base pairs of DNA as are evidenced by: hyperchromism in UV absorption band of DNA, sharp increase in specific viscosity of DNA and decrease in the fluorescence of TBHQ solutions in the presence of increasing amounts of DNA. Also peak current decrease, positive shift in the cyclic voltammetry (CV) and differential pulse voltammetry (DPV) are other evidences to indicate that, TBHQ is able to be intercalated in the DNA base pairs.     

Study on the interaction of food colourant quinoline yellow with bovine serum albumin by spectroscopic techniques

The interaction of a food colourant, quinoline yellow (Qy), and bovine serum albumin (BSA) was investigated by spectrophotometry, spectrofluorometry, FT-IR and circular dichroism (CD) techniques. The experimental results indicated that the quenching mechanism of BSA by the dye was a static procedure. Various binding parameters were evaluated. The negative value of ΔH, negative value of ΔS and the negative value of ΔG indicated that van der Waals force and hydrogen bonding play major roles in the binding of Qy and BSA. Based on Forster's theory of non-radiation energy transfer, the binding distance, r, between the donor (BSA) and acceptor (Qy) was evaluated. The results of CD and UV-vis spectroscopy showed that this dye could bind to BSA and the conformation of BSA changed.     

Spectroscopic studies on the interaction of sodium benzoate,a food preservative,with calf thymus DNA

The interaction between sodium benzoate (SB) and calf thymus DNA in simulated physiological buffer (pH 7.4) using acridine orange (AO) dye as a fluorescence probe, was investigated by UV–Vis absorption, fluorescence and circular dichroism (CD) spectroscopy along with DNA melting studies and viscosity measurements. An expanded UV–Vis spectral data matrix was resolved by multivariate curve resolution-alternating least squares (MCR−ALS) approach. The equilibrium concentration profiles and the pure spectra for SB, DNA and DNA–SB complex from the high overlapping composite response were simultaneously obtained. The results indicated that SB could bind to DNA, and hydrophobic interactions and hydrogen bonds played a vital role in the binding process. Moreover, SB was able to quench the fluorescence of DNA−AO complex through a static procedure. The quenching observed was indicative of an intercalative mode of interaction between SB and DNA, which was supported by melting studies, viscosity measurements and CD analysis.     

Effects of pulsed electric field treatment on a bovine serum albumin–dextran model system,a means of promoting the Maillard reaction

Effects of pulsed electric field treatment on browning intensity, antioxidant activity, protein patterns and chemical structure of the bovine serum albumin–dextran copolymer were investigated. Results showed Maillard reaction between bovine serum albumin and dextran was significantly accelerated when the electric field intensity was higher than 10 kV/cm, which was proved by changes in A₂₉₄, browning, antioxidant activity and electrophoresis tests. At the same time, pronounced changes of chemical structure were found by circular dichroism test. The α-helix, β-sheet, β-turns and random coil were changed from approximately 42.6%, 1.9%, 17.5% and 33.9% to 14.5%, 33.0%, 21.2% and 30.2%, respectively, after treatment at 20 kV/cm for 7.35 ms. All data indicated that pulsed electric field was a means to promote Maillard-based copolymerisation.     

Mechanistic and conformational studies on the interaction of food dye amaranth with human serum albumin by multispectroscopic methods

The mechanism of interaction between food dye amaranth and human serum albumin (HSA) in physiological buffer (pH 7.4) was investigated by fluorescence, UV–vis absorption, circular dichroism (CD), and Fourier transform infrared (FT-IR) spectroscopy. Results obtained from analysis of fluorescence spectra indicated that amaranth had a strong ability to quench the intrinsic fluorescence of HSA through a static quenching procedure. The negative value of enthalpy change and positive value of entropy change elucidated that the binding of amaranth to HSA was driven mainly by hydrophobic and hydrogen bonding interactions. The surface hydrophobicity of HSA increased after binding with amaranth. The binding distance between HSA and amaranth was estimated to be 3.03 nm and subdomain IIA (Sudlow site I) was the primary binding site for amaranth on HSA. The results of CD and FT-IR spectra showed that binding of amaranth to HSA induced conformational changes of HSA.     

Effect of luteolin on xanthine oxidase: Inhibition kinetics and interaction mechanism merging with docking simulation

Xanthine oxidase (XO) catalyses hypoxanthine and xanthine to uric acid in human metabolism. Overproduction of uric acid will lead to hyperuricemia and finally cause gout and other diseases. Luteolin is one of the major components of celery and green peppers, its inhibitory activity on XO and their interaction mechanism were evaluated by multispectroscopic methods, coupled with molecular simulation. It was found that luteolin reversibly inhibited XO in a competitive manner with inhibition constant (K_i) value of (2.38 ± 0.05) × 10⁻⁶ mol l⁻¹. Luteolin could bind to XO at a single binding site and the binding was driven mainly by hydrophobic interactions. Analysis of synchronous fluorescence and circular dichroism spectra demonstrated that the microenvironment and secondary structure of XO were altered upon interaction with luteolin. The molecular docking results revealed luteolin actually interacted with the primary amino acid residues located within the active site pocket of XO.     

Impact of sorbitol on the thermostability and heat-induced gelation of bovine serum albumin

The influence of sorbitol (0–40 wt.%) on the thermal denaturation and gelation of bovine serum albumin (BSA, pH 7.0) in aqueous solution has been studied. The effect of sorbitol on heat denaturation of 0.5 wt.% BSA solutions was measured using ultrasensitive differential scanning calorimetry. The unfolding process was irreversible and was characterized by the thermal denaturation temperature (T_m). As the sorbitol concentration increased from 0 to 40 wt.%, T_m increased from 73.0 to 80.9 °C. The rise in T_m was attributed to the increased thermal stability of the globular state of BSA relative to its native state. The dynamic shear rheology of 4 wt.% BSA solutions containing 200 mM NaCl was monitored as they were heated from 30 to 90 °C at 1.5 °C min⁻¹, held at 90 °C for 120 min, and then cooled back to 30 °C at −1.5 °C min⁻¹. Sorbitol increased the protein gelation temperature (ΔT_gel +10 °C for 40 wt.% sorbitol), decreased the isothermal gelation rate at 90 °C, but increased the final shear modulus of the gels cooled to 30 °C. The impact of sorbitol on gel characteristics was attributed to its ability to increase protein thermal stability, increase the attractive force between proteins and decrease the protein–protein collision frequency.     

Structure-affinity relationship of bovine serum albumin with dietary flavonoids with different C-ring substituents in the presence of Fe ion

The relationship of four dietary flavonoids, quercein (QU), luteolin (LU), taxifolin (TA) and (+)-catechin (CA), with different C-ring substituents binding with bovine serum albumin (BSA) have been investigated in the absence and presence of Fe³⁺ by means of spectroscopic methods. The quenching constant (K_SV), binding constant (K_a), binding site number (n) and spatial-distance (r) of flavonoids with BSA were calculated. The results indicated that hydroxyl group at 3-position and C2–C3 double bond affected the binding affinities between flavonoids and BSA. The values of the binding affinities were in the order: QU > CA > TA > LU. The presence of Fe³⁺ affected the interactions between flavonoids and BSA significantly, and the influence was distinct for the flavonoids with different C-ring structures. The binding affinities of QU, LU and CA for BSA were increased about 0.85%, 41.3% and 56.8% in the presence of Fe³⁺, probably because of the formation of QU–Fe³⁺–BSA complex, Fe³⁺–LU complex and the conformational change of BSA induced by Fe³⁺, respectively. The binding affinities of TA for BSA were decreased about 20.7%, mainly because of the existence of competitive binding between TA and Fe³⁺ with BSA. However, the quenching mechanism for QU, LU, TA and CA to BSA were based on static quenching combined with non-radiative energy transfer irrespective of the absence or presence of Fe³⁺ ion.     

Preparation of size-controlled bovine serum albumin (BSA) nanoparticles by a modified desolvation method

The size effect of nanomaterials is of major interest, since it may affect their bioavailability and toxicity. In this study, bovine serum albumin (BSA) nanoparticles were prepared using a modified desolvation method. Bare BSA nanoparticles and calcium (Ca)-loaded BSA nanoparticles were fabricated at the targeted sizes, 100, 400, and 800 nm. The mean diameters of the prepared BSA nanoparticles were 125, 393, and 713 nm; those of the Ca-BSA nanoparticles were 260, 353, and 919 nm. The surface-area-to-volume-ratios of the prepared BSA nanoparticles were 4.82, 1.53, and 1.03 nm⁻¹; those of the Ca-BSA nanoparticles were 2.34, 1.72, and 0.90 nm⁻¹. The size and the surface-area-to-volume-ratio of the BSA nanoparticles were controlled by adjusting BSA concentration, pH, and NaCl content, which affected the coagulation of the BSA molecules. The surface-area-to-volume-ratio is a more useful parameter than the mean diameter of particles for comparing effectiveness of nanoparticles.     

Spectroscopic investigation on the interaction of 3,7-dihydroxyflavone with different isomers of human serum albumin

The interaction mechanism of 3,7-dihydroxyflavone (3,7-diHF) and human serum albumin (HSA) was investigated by fluorescence quenching, fluorescence enhancement, steady-state and time-resolved fluorescence emission and UV-vis absorption spectrometry. The binding site of 3,7-diHF on protein was determined by investigating the spectroscopic properties of 3,7-diHF-HSA complex at pH 7.4 and pH 3.5 individually, and confirmed by the site marker competitive experiments. The binding parameters of 3,7-diHF-HSA complex were estimated by fluorescence quenching experiments, and the data were in good agreement with the results obtained from fluorescence enhancement measurements. A remarkable increase in the fluorescence anisotropy values suggested that 3,7-diHF bound at a motional restricted pocket on HSA. The results indicated that 3,7-diHF, in anionic form, was bound within the hydrophobic pockets of the subdomain IIA of HSA (site I), and stabilised mainly by electrostatic force and ionic interactions. The binding mode of drug-protein was discussed based on above experimental results.     

Effect of dielectric barrier discharge (DBD) plasma on the structure and antioxidant activity of bovine serum albumin (BSA)

This study was aimed to determine the influence of dielectric barrier discharge (DBD) plasma with a plasma intensity (20 and 40 kV) and treatment times (0, 2, 4, 6 and 8 min) on the physicochemical, structural and antioxidant properties of bovine serum albumin (BSA) solution. In results, the free sulphydryl content, pH and free amino group contents, while carbonyl groups and surface hydrophobicity were increased after the plasma treatment. After plasma treatment, there is also an increase in the DPPH and FRAP assay that was associated with the changes in the structure of the peptides chain. The complementary techniques were employed to identify the protein structural modifications by plasma treatment. These changes were more severe at the most extended treatment duration and plasma intensity. The high energetic and oxidising species carried by plasma may have significant associations on the structural and physical properties of BSA.     

纤维素金属螯合亲和膜的制备及其对牛血清白蛋白的吸附研究

以纤维素分析滤纸为载体、环氧氯丙烷(EPI)为交联活化剂、亚氨基二乙酸(IDA)为配基、铜离子为金属螯合离子,可制得Cu2 -IDA型固定化金属螯合膜。实验表明,滤纸先用4mol／L的NaOH浸润45min,再在75℃水浴中活化反应45min,所得亲和膜环氧基密度可达3.97μmol／cm2。最佳配基偶联反应条件为:25mgIDA／cm2膜、60℃、15h时可获得对Cu2 最大螯合量。牛血清白蛋白(BSA)等温吸附线基本符合Langmuir形式,经曲线拟合得最大吸附量为59.52mg/g干膜。     

光谱法研究绿原酸和牛血清白蛋白的相互作用

为了解绿原酸和牛血清白蛋白的相互作用,在模拟动物生理条件下,采用荧光光谱和紫外-可见吸收光谱结合Stern-Volmer方程、double-reciprocal方程和热力学公式来研究绿原酸与牛血清白蛋白相互作用特征。结果表明:绿原酸和牛血清白蛋白在298K和310K两个温度下的结合常数分别为1.869×105L·mol-1和1.574×105L·mol-1;结合位点分别为1.18和1.16;且热力学参数ΔH0、ΔS0、ΔG0;结合距离小于7nm。因此,绿原酸对牛血清白蛋白有较强的荧光静态猝灭作用,符合静态猝灭过程,结合力为疏水作用。     

荧光光谱法结合分子对接探究pH对姜黄素与牛血清白蛋白结合的影响

目的 采用荧光光谱法结合分子对接探究姜黄素(curcumin,CUR)与牛血清白蛋白(bovine serum albumin,B SA)在不同pH条件下相互作用。方法 通过荧光光谱法计算结合常数和热力学参数分析CUR对BSA荧光猝灭作用和机制;采用位点Marker和分子对接分析结合位点。结果 CUR与BSA结合形成了复合物,产生内源性荧光猝灭作用,属于静态猝灭。不同pH条件下的结合作用力不同,但结合位点数目均为1。由同步荧光可知,色氨酸残基附近疏水性增强,说明与CUR结合后BSA构象出现了收缩,结合位点靠近色氨酸。位点Marker实验证明pH影响CUR与BSA结合位点,分子对接结果表明, pH 7.4时CUR与BSA的结合位点位于Sudlow’s site I附近。结论 本研究表明pH影响CUR与BSA的结合反应,为CUR的活性保护及蛋白基递送载体研究提供理论支持。     

Kinetic Study of the Quenching Reaction of Singlet Oxygen by Common Synthetic Antioxidants (tert-Butylhydroxyanisol, tert-di-Butylhydroxytoluene, and tert-Butylhydroquinone) as Compared with α-Tocopherol

ABSTRACT: Effects of synthetic phenolic antioxidants (BHA, BHT, and TBHQ) on the methylene blue (MB) sensitized photooxidation of linoleic acid as compared with that of α‐tocopherol have been studied. Their antioxidative mechanism was studied by both ESR spectroscopy in a 2,2,6,6‐tetramethylpiperidone (TMPD)‐methylene blue (MB) system and spectroscopic analysis of rubrene oxidation induced by a chemical source of singlet oxygen. Total singlet oxygen quenching rate constants (k_ox?Q+k_q) were determined using a steady state kinetic equation. TBHQ showed the strongest protective activity against the MB sensitized photooxidation of linoleic acid, followed by BHA and BHT. TBHQ (1 × 10^?3 M) exhibited 86.5% and 71.4% inhibition of peroxide and conjugated diene formations, respectively, in linoleic acid photooxidation after 60‐min light illumination. The protective activity of TBHQ against the photosensitized oxidation of linoleic acid was almost comparable to that of α‐tocopherol. The data obtained from ESR and rubrene oxidation studies clearly showed the strong singlet oxygen quenching ability of TBHQ. The k_ox?Q+k_q of BHA, BHT, and TBHQ were determined to be 3.37 × 10⁷, 4.26 × 10⁶, and 1.67 × 10⁸ M^?1 s^?1, respectively. The k_ox?Q+k_q of TBHQ was within the same order of magnitude of that of α‐tocopherol, a known efficient singlet oxygen quencher. There was a high negative correlation (r² = ?0.991) between log (k_ox?Q+k_q) and reported oxidation potentials for the synthetic antioxidants, indicating their charge‐transfer mechanism for singlet oxygen quenching. This is the 1st report on the kinetic study on k_ox?Q+k_q of TBHQ in methanol as compared with other commonly used commercial synthetic antioxidants and α‐tocopherol.     

Effects of the attachment of small molecules by carbodiimide-mediated condensation on the physicochemical and functional properties of bovine serum albumin

The effects of attaching three small molecules, namely N-butylamide, putrescine and lysine, via the carboxyl groups of bovine serum albumin on its physicochemical and functional properties ere studied. To levels of attachment ere achieved by choice of reaction time. All modified samples had high isoelectric points and ere highly positive hen separated electrophoretically. Partially and extensively modified samples behaved differently in their pH titration curves, their gelation properties and the hipping properties of their lysyl derivatives, in that partially modified samples had high values compared ith the control and extensively modified samples had loer values. This as explicable by to theories: either there is increased electrostatic attraction beteen molecules hose isoelectric points are closer to neutrality, or there is a midpoint here a partial degree of conformational disruption results in superior functional properties. The level of conformational disruption in the extensively modified samples as greater than the optimum, hich resulted in impaired functional properties. An EDC control sample produced ithout added nucleophile as extensively cross-linked intra- or intermolecularly and had impaired functional properties.     

The influence of flavonoids on the binding of pantoprazole to bovine serum albumin by spectroscopic methods: With the viewpoint of food/drug interference

The interaction of pantoprazole to bovine serum albumin (BSA) has been investigated with and without four popular 5,7,3',4'-hydroxy-substituted flavonoids, quercetin, luteolin, taxifolin and (+)-catechin. The presence of flavonoids decreased binding constants of pantoprazole with BSA from 39.7% to 93.8%, which depended on flavonoid structures. Analysis of infrared spectroscopy (IR) and circular dichroism (CD) showed the binding of pantoprazole to BSA caused apparent change in secondary structure of BSA. The calculated values of spatial-distance indicated the existence of quercetin, luteolin and taxifolin may compete with pantoprazole binding to BSA, while the existence of (+)-catechin possibly formed ternary pantoprazole-BSA-(+)-catechin complex. However, all the fluorescence quenching was initiated by static quenching procedure irrespective of the absence or presence of flavonoids, while van der Waals force and hydrogen bonds played major roles for pantoprazole-BSA association. All above results may have relevant consequence in rationalising the interferences of common food to gastric ulcer treatments.